Plenums or other chambers are commonly used to receive and at least temporarily store fragmented or particulated material such as, for example, in various materials handling apparatus. One type of apparatus in which the present invention is particularly suitable is a rotary drum air classifier system wherein materials are deposited in a suitable plenum after being separated in and discharged from a rotary drum air classifier. Such a system is fully described in U.S. patent application Ser. No. 580,373, filed May 22, 1975 and now abandoned.
It will be understood that very often such systems are used to classify municipal waste which includes a mixture of materials of various densities containing various amounts of moisture. When the moisture content of a mixture is relatively high, it has been found that the various materials in the mixture will adhere together or coalesce. This is particularly true in the plenum where the materials may be deposited to a substantial height, the weight thus severely compacting the materials in the bottom portion of the plenum.
Adjacent the bottom of the plenum is usually located a discharge conveyor. A closure member normally closes a discharge opening in the lower end of the plenum. When the member is moved to open position, materials will fall through the opening onto the discharge conveyor. However, it has been found that sometimes the opening becomes clogged by the moisture-containing materials. This usually requires shutdown of the apparatus until the situation is corrected.
An attempt was made to seal the lower end of the plenum with discharge means in the form of one or more screw conveyors which would be activated to remove the packed materials from the plenum. Such a device, combined with moisture-removing means, was disclosed in U.S. patent application Ser. No. 647,267, filed Jan. 5, 1976 and now abandoned. However, screw conveyors were also found to be unsuitable for removing packed moisture-containing materials when used for this purpose.